Absorbent articles such as disposable diapers, adult incontinent pads, sanitary napkins and the like are generally provided with absorbent members, fibrous web structures which comprise entangled masses of fibers, to receive and retain bodily fluids. In order for such absorbent articles to function efficiently, the absorbent members must quickly acquire bodily fluids into the structure from the point of application and subsequently distribute the fluids within and throughout the absorbent member to provide maximum liquid containment. In addition, the absorbent members should be capable of retaining liquids when placed under loads. Prior art attempts to improve the effectiveness of such absorbent members have included distributing particles of absorbent gelling material throughout or in portions of the absorbent member. For example, U.S. Pat. No. 4,610,678, entitled "High-Density absorbent Structures" which issued to Paul T. Weisman and Stephen A. Goldman on Sep. 9, 1986, discloses absorbent members wherein particles of absorbent gelling material (hydrogel) are dispersed in an air-laid web of hydrophilic fibrous material and compressed to a particular density. In addition, U.S. Pat. No. 4,673,402, entitled "Absorbent Articles With Dual-Layered Cores" which issued to Paul T. Weisman, Dawn I. Houghton and Dale A. Gelleft on Jun. 16, 1987, discloses a dual-layer absorbent core wherein an absorbent acquisition layer overlays a lower fluid storage layer that consists essentially of a uniform combination of hydrophilic fibrous material and discrete particles of absorbent gelling material. These patents are incorporated herein by reference.
Other references which disclose dual-layer absorbent members in combination with absorbent gelling materials are PCT Published Applications WO 91/11162, WO 91/11163, and WO 91/11165, each having been published on Aug. 8, 1991. These published patent applications were each filed in the name of the Procter & Gamble Company, and each is hereby incorporated herein by reference.
U.S. Pat. No. 5,047,023, entitled "Absorbent Members Having Low Density and Basis Weight Acquisition Zones", which issued to Charles J. Berg on Sep. 10, 1991, and U.S. Pat. No. 4,834,735, entitled "High Density Absorbent Members Having Lower Density and Basis Weight Acquisition Zones", which issued to Miguel Alemany and Charles J. Berg on May 30, 1989, disclose absorbent articles incorporating such absorbent gelling materials into absorbent members which have selective densification. These patents are also incorporated herein by reference.
Absorbent gelling materials are polymeric materials which are capable of absorbing large quantities of liquids such as water and body wastes relative to their weight, and which are further capable of retaining such absorbed liquids under moderate pressures. These absorption characteristics of absorbent gelling materials make them especially useful for incorporation into absorbent articles such as disposable diapers, adult incontinent pads, sanitary napkins and the like. However, in spite of the extremely high absorption capacities of such absorbent gelling materials, their performance when used in disposable absorbent articles has still not been optimized.
The effectiveness of absorbent gelling materials in disposable absorbent articles is quite dependent upon the form, position, size, and/or manner in which the particles of absorbent gelling material are incorporated into the absorbent member. One way to theoretically improve the absorbent capacity of an absorbent article would be to increase the level of absorbent gelling material in the absorbent member. Unfortunately, however, the effectiveness of absorbent members containing higher concentrations of particles of absorbent gelling material can be adversely affected by a phenomenon called gel blocking. The term "gel blocking" describes a situation that occurs when a particle of absorbent gelling material is wetted. the surface of the particles swelling so as to inhibit liquid transmission into the interior of the absorbent member. Wetting of the interior of the absorbent member, therefore, takes place via a very slow diffusion process. In practical terms, this means that acquisition of liquids by the absorbent member is much slower than the discharge of the liquid to be absorbed, and leakage from the absorbent article may take place well before the particles of absorbent gelling material in the absorbent member are fully saturated or before the liquid can diffuse or wick past the "blocking" particles into the rest of the absorbent member. Often, the storage capacities of areas of the absorbent member remote from the liquid deposition go un-utilized.
Another reason why many absorbent articles are subject to leakage is inability to absorb second and subsequent discharges of fluid even if the first discharge has been effectively absorbed. After a discharge of fluid occurs, the fluid tends to remain situated in the region proximate to the discharge. This is due to the inability of the absorbent core to transport discharged fluid away from the region of discharge once the absorbent capacity of that region has reached the saturation point.
In absorbent members incorporating comparatively higher concentrations of absorbent gelling materials in the interest of higher storage capacity, the problem is aggravated by the fact that in order to increase the amount of absorbent gelling material while maintaining a constant thickness, less hydrophilic fibrous material can be included in the storage layer. The role of the fibrous material in providing wicking capability within the absorbent gelling material-containing storage layer and maintaining a fiber/absorbent gelling material matrix is greatly reduced, necessitating some other method of acquiring and distributing fluid within the absorbent member to regions of the storage layer remote from the liquid infusion.
Thus, it would be advantageous to provide a multi-layer absorbent member that more quickly acquires and distributes liquids within itself while minimizing gel blocking in the storage layer during the liquid acquisition phase. It is therefore a primary objective of the present invention to provide improved absorbent members which are especially effective and efficient in their use of absorbent gelling materials.
It is a further object of the present invention to provide absorbent members of improved capacity and efficiency by utilizinq an acquisition layer of selectively densified, hydrophilic fibrous material to effectively acquire and distribute fluid to a storage layer which includes a comparatively higher concentration of absorbent gelling material.